IDOT presented the challenge of developing a viable, economical solution to accelerate the replacement of aging bridge infrastructure in the United States. An industry task force has developed a bent barrel truss beam for short-span bridges, which is formed in the factory and pre-assembled. A specific platform and installed on site within hours or days.
Editor’s note: This article is based in part on a speech at the 2019 AISC World Steel Bridge Seminar held in St. Louis on April 3, 2019.
It is no secret that the US infrastructure is about to be replaced. When the I-35 Mississippi River Bridge in Minneapolis collapsed, killing 13 people, the entire country took notice.
Two years later, the “American Recovery and Reinvestment Act” provided nearly $50 billion in funding for transportation infrastructure to support the maintenance and long-term transformation investments required by communities in each state. The maintenance and replacement of infrastructure are goals that both parties seem to agree on.
According to the Bureau of Transportation Statistics, the total number of bridges in the United States in 2019 exceeded 617,000, and only 279,582 were in good condition, accounting for 44%. In 2016, more than 56,000 (9.1%) US bridges were classified as structural defects. *
time is life. According to the 2017 American Society of Civil Engineers (ASCE) statement, four out of ten people are over 50 years old.
Dr. Alison Premo Black, chief economist of the American Road and Transportation Builders Association (ARTBA), said: “At the current rate, it will take more than 50 years to repair the structurally defective bridges in the United States.”
Dr. Karl Barth of the Department of Civil and Environmental Engineering at West Virginia University said: “The biggest demand is for the short-span category of 140 feet or less.” He added that nearly half of the structurally defective bridges are short-spans. Span category. A short-span bridge is defined as a bridge where the distance between two intermediate supports is shorter than 140 feet.
In seeking new, better, faster, and cheaper bridge replacement methods to help solve the US infrastructure crisis, IDOT posed a challenge, requiring the development of a viable and economical solution to replace outdated bridges Infrastructure to shorten the short span structure by 80 feet.
Researchers at West Virginia University started with a typical welded trapezoidal box, but made it with a bending machine to save cost and time. Manufactured by Greiner Industries. Image courtesy of the Short Span Bridge Alliance.
The Federal Highway Administration has tasked us to develop an economical system for accelerating the construction of short-span bridges,” Bart said. “The goal is to use standard, usually available board widths of 84 inches, 96 inches, etc. “The process must also be compatible with mass production to avoid customization costs.
What is a system? It is just a simple steel truss beam (with twists) with a precast concrete deck.
Bart said: “We used a standard steel trapezoidal box for winding, but it was made by a bending machine instead of a traditional welding method.” “With bending forming, it can be produced in about 30 to 40 minutes. The characteristics of a short span.”
The beam type is a common American trapezoidal beam with a slope ratio of 1-4 and a bending radius of 5T, Barth explained. “We don’t think we need to compress the flanges too much. We fixed them to 6 inches wide. We just need enough strength to hold the studs until we place the deck there.”
The plate barrel beam (PBFTG) formed by bending is galvanized to extend the service life, and then a concrete panel is laid on the top. “Our standard is to hot-dip galvanize them to provide more than 60 years of protection.
“This is not a big innovation. But it is a way to save costs in the short-term market. Larger, more complex bridge geometries with closed-section barrels are ideal for welding applications. The problem is that you cannot economically reduce this technology to 40, 60, 80 feet. The short-span bridge market,” Bart concluded.
The module can be pre-assembled or assembled on site. The components are connected with a longitudinally closed gate using ultra high performance concrete (UHPC).
During the research phase, the bending of the press brake was performed by Greiner Industries of Grey Joy, Pennsylvania. The manufacturer formed the barrel elbow on the 2,750-ton, 40-foot-long Baykal bending machine that he already had, and then purchased the bending machine. Work with extension tools.
The manufacturer of Greiner Industries, Pennsylvania, formed the cylinder elbow on a 2,750-ton, 40-foot-long Baykal brake press. The manufacturer also installed a laser alignment tool that was pointed at the internal bending target to ensure that the workpiece was perfectly aligned with the punch.
The manufacturer also has 26 feet. A brake that can bend a 60-foot-thick 3/4-inch-thick plate with 34 feet, but it uses a 40-foot-long brake because it provides many advantages for a 40-foot-long brake. Bridge span.
The opening of the bed can be adjusted from 3 to 17 inches. “We can bend thick plates as thick as 1-1/4 inches over the entire 40-foot range,” said Bruce Sine, manager of the rolling and forming department. “Because it is a machine, we own the entire printing press.”
The bending machine is also adapted to the multiple bends required to form the bucket. “Once you enter multiple bends, it becomes interesting because if you have flanges, you have to flip them to bend those flanges, and there must be enough space to reach the second bend without Anything else will come across,” Sine said. “When you use a tandem press, depending on its throat, it may hit the rear frame, so you won’t be able to bend long legs on it. In the case of a 40-foot length, we have a gap of 2 feet, so We have enough clearance to bend the flange.
Greiner also installed a laser alignment tool that points to the internal curved target. “We want to make sure that the work is perfectly aligned with the punch. This way, you can really determine where to bend. Much more accurate than a tape measure.”
The bed of the bending machine is equipped with a mechanical crown adjustment device. “Crowding is not a problem; you just need to adjust the bed for this. In fact, if one side hits harder than the other, you can actually adjust the Y1 and Y2 axes.”
Sine said that in general, the job is not difficult. “Once dialed in, it is easy to proceed.”
The research team conducted extensive fatigue tests on the beams to calculate the yield capacity at various plate thicknesses. The team used 84 inches wide by 7/16 inches wide. Plate (50 and 79-KSI) steel is used in a series of research tests at the university. Bart said: “This is the largest beam we can build and test for failure with a 330 kp actuator to assess the load-bearing capacity.”
The test showed the “sweet spot” for each board thickness (7/16 inch, 1/2 inch, 5/8 inch) and width (60 inches to 120 inches long). The depth they finally determined is the depth of the superstructure of the beam after verifying the bearing capacity of the beam. Suitable for spans up to 60 feet and 1/2 inch. Board works. For longer spans, up to 80 feet, 5/8 inch thick plates are required.
“At a certain depth, you can get the maximum capacity of the part. Once you set the flange width and slope, and select the depth on a common rolled steel plate, all geometric shapes will be generated from this.” He said .
The team tested the fatigue properties of galvanized and uncoated steel to see if the selected bending radius would cause problems. Then they tested the modular system with closed casting to evaluate the deck. They evaluated the capabilities of the modules using casting and deck systems as well as support requirements and deflection. “We have been testing this for seven years. Therefore, the system has been fully reviewed.” Barth said.
PBFTG meets the requirements of the American Association of Highway and Transportation Officials (AASHTO).
Funding from the Innovative Bridge Research and Deployment (IBRD) program of the Federal Highway Administration (FHWA) of the United States Department of Transportation laid the foundation for the first installation of the modular PBFTG system in the United States.
FHWA received a $350,000 grant from Brian Keierleber of Engineer PE from the IBRD program to replace the Amish Sawmill Bridge in Fairbank, Buchanan County, Iowa.
Keierleber said: “Standardization is of great significance in the short-term market.” “We don’t want to customize everybody as a work of art. If you need 40 feet. Girder, you just need to go to this table and choose a 36-foot span The girder is fine. There is no reason to redesign it.” The standard design is 20 to 80 feet.
“We are talking about speeding up construction. The superstructure was installed in 20 minutes. I have never seen a 20-minute bridge before.” Bart said.
226 bridges are maintained in St. Clair County, Michigan. Among them, 20 people are in severe or severe condition, 21 people are in bad condition, and two people have weight restrictions that prohibit truck traffic. Due to conditions, two of them are prohibited from passing through. “They can’t keep up. This is common in the United States.”
Both bridges in St. Clair County have weight restrictions that prohibit trucks from passing. The two-lane road has more than 16,000 intersections and is a critical path to Marine City. They were built in 1953 and have served for 65 years. No recoating or other maintenance of the steel beams was performed.
TEG Engineering was hired as an engineer for two bridge superstructures in the summer of 2018 to replace them. The company designs precast bridges to minimize the impact of on-site construction activities on mobility.
“The bridge must be simple, durable, compatible with AASHTO design and sustainable,” said Guy Nelson of TEG Engineering PE. “If these are one-offs, then you will never get an affordable system. We have to implement affordable bathtub girder. And we are doing this throughout the United States.”
The cost comparison shows that the cost of a conventional steel bridge with a hot mix asphalt (HMA) overlay on a galvanized steel deck is US$75,000; the prefabricated box culvert system will cost US$63,000; and the HMA entry price of the PBFTG system is US$57,000, and The road closure time is the shortest.
Nielsen said: “We purchased the steel beams, galvanized sheets and studs formed by the bending machine, and hired local qualified prefabricators to assemble the entire bridge.” Manufacturing of PBFTG (galvanized, metal manufacturing And concrete deck pouring) takes about two months, so it started two months before the bridge was demolished.
On one of the bridges, the county was able to use its own excavator equipment to install a 35-foot span of equipment for the bridge, and only a crane was needed to install 45 feet. Straddle the second bridge.
When there is a deflection problem or a shallower box is needed to match the previous system, the flange-in box has a wider bottom flange to increase the capacity and rigidity of the entire system.
The replacement of the superstructure was completed in four days. It took two days to demolish the existing bridge and two days to repair the concrete abutment. The PBFTG superstructure itself was installed on the fourth day of four hours. Nelson said: “The beam was brought in at 8 am and assembled on site at noon.”
Pour polymer concrete into the bridge deck joints, and then pour the epoxy coating. Then, the asphalt layer covers the entire deck. Finally, the guardrail was installed. The total completion time is 10 working days.
*The term “structural defects” was redefined in 2018, and 5.5% of U.S. bridges are now classified as structural defects. In addition, the agency no longer tracks bridges that were previously called “functionally obsolete.”
Kate Bachman is the editor of Stamp Magazine. She is responsible for the overall editorial content, quality and direction of STAMPING Journal. In this position, she edits and writes technology, case studies and feature articles; publishes monthly reviews; and is responsible for managing regular departments in the magazine.
Bachman has over 20 years of writer and editor experience in manufacturing and other industries.
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Post time: Jan-29-2021